The present invention relates to locking apparatus for downhole tools, and more particularly, to a pressure activated locking slot assembly.
Typically, when tools are run into the well bore, a mandrel is held in the run-in-hole position by interaction of a lug with a J-slot. To move the tool out of the run-in-hole position generally involves the application of torque and longitudinal force. Such an arrangement can be problematic in offshore or highly deviated sections of a well bore, where dragging forces on the tool string may create difficulty in estimating the proper torque to apply at the surface to obtain the desirable torque at the J-slot. A continuous J-slot wraps all the way around the mandrel and typically has two lugs, so that the direction of torque applied need not be reversed in order to actuate. Rather, the tool may simply be picked up and put back down to cycle.
A problem may arise when running such a tool into an offshore or highly deviated well bore. Dragging of the tool string on the well bore may cause the mandrel move relatively upwardly and rotate with respect to the drag block assembly sufficiently to result in premature actuation of the J-slot assembly. If such premature actuation occurs, subsequent downward load on the tool string may rupture the tool elements, or the tool elements may be damaged by dragging along the well bore. In addition, premature actuation may result in the tool string jamming in the well bore.